In modern internal combustion engines, use is made of devices for variably adjusting the control times of gas-exchange valves in order to be able to variably adjust the phase relationship between the crankshaft and the camshaft in a defined angle range between a maximum early position and a maximum late position. For this purpose, the device is integrated into a drivetrain which serves to transmit torque from the crankshaft to the camshaft. Said drivetrain may for example be realized as a belt drive, chain drive or gearwheel drive. The devices have a hydraulic actuating drive composed of at least two pressure chambers which act counter to one another. The pressure medium flows from and to the pressure chambers are controlled by means of a hydraulic control valve. Control valves of said type have a hydraulic section, via which the pressure medium is conducted, and an actuating drive, which controls the hydraulic section. Here, so-called plug-in valves are known which are arranged in a receptacle of the cylinder head or of the cylinder head cover. The actuating drive of said control valves is fixedly connected to the hydraulic section. Also known are so-called central valves whose hydraulic section is held in the device and rotates with the latter. The actuating drive is fixedly connected to the cylinder head or to the cylinder head cover, with the positioning movement being transmitted to the hydraulic section by means of a plunger rod.
A control valve of said type and a device are known for example from U.S. Pat. No. 6,971,353 A1. The device comprises a drive output element which is arranged so as to be rotatable with respect to a drive input element, with the drive input element being drive-connected to the crankshaft, and the drive output element being rotationally fixedly connected to the camshaft. The device is delimited in the axial direction by means of in each case one side cover, with one of the side covers supporting a drive input wheel. The drive output element, the drive input element and the two side covers delimit a plurality of pressure spaces, with each of the pressure spaces being divided by means of a vane into two pressure chambers which act counter to one another. By supplying pressure medium to and discharging medium from the pressure chambers, the vanes within the pressure spaces are moved, thereby bringing about a targeted rotation of the drive output element with respect to the drive input element and therefore of the camshaft with respect to the crankshaft.
The device is rotationally fixedly connected to the camshaft by means of a central screw which simultaneously serves as a control valve. The control valve has a valve housing into which are formed two central and axially running cavities which are axially offset with respect to one another. Arranged in one of the cavities is a control piston which can be moved axially in the cavity, counter to the force of a spring, by means of an electromagnetic actuating unit. The second cavity communicates with the interior, which is acted on with pressure medium, of the camshaft. Pressure medium can be supplied to a supply connection, which is arranged in the region of the first cavity, of the control valve via the second cavity and via radial bores axial bores, which open out into said cavity, within the drive output element. Pressure medium is supplied to the first or second pressure chambers, and pressure medium is discharged from the other pressure chambers, as a function of the position of the control piston within the first cavity.
A disadvantage of said embodiment is the complex structure of the control valve. In particular, the formation of two cavities into the valve housing, which are axially offset with respect to one another and are hydraulically separated from one another by material of the valve housing, requires complex and expensive machining steps. Furthermore, dirt particles present in the interior of the camshaft can penetrate into the control valve and impair its functional capability. Furthermore, pressure peaks which are generated in the device on account of the alternating torque acting on the camshaft can propagate into the pressure medium circuit and cause damage to connected loads or the pressure medium pump.